Convex-walled,cusped,vented,bistable flueric amplifier



United States Patent 1111 3,550, 7

[72] Inventor Turgut Sarpkaya [56] References Cited C C UNITED STATES PATENTS [211 P 759,595 3,030,979 4/1962 Reilly 137/815 [221 FM Sept-3,1968 3,181,546 5/1965 B00th.... l37/8l.5 [45] i 3,232,533 2/1966 Boothe l37/81.5X [731 Ass'gnee heun'teds'ammmema 3,273,377 9/1966 Testermanetal. 137/81.5X representedbYhFsec'earYmhe 3,283,767 11/1966 Wright 137/815 Army-bymesneass'gnmem 3,340,884 9/1967 Warrenetal... 137/815 3,405,736 /1968 Readeretal 137/815 Primary Examiner-Samuel Scott Attorneys-Harry M. Saragovitz, Edward J. Kelly, Herbert 54 CONVEX-WALLED, cusprzn, VENTED, BISTABLE Edgerto" FLUERIC AMPLIFIER 7 Chums 5 Drawing Figs ABSTRACT: A convex-walled, cusped, vented bistable flueric [52] U.S. Cl 137/815 amplifier having critical geometry and dimensional ratios ina [51] Int. Cl Fc l/08 narrow range to yield a nearly ideal pressure recovery Fieldof Search l37/8l.5 response characteristic.

PATENTEU BECZQIQYG 3350,6707

FIGI

CONVEX-WALLED. CUSPED. VENTED. BISTABLE FLUERIC AMPLIFIER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention'relates to a fluid handling device in which the fluid flow is affected by the Coanda effect, and moreparticularly to a bistableflueric amplifier.

2. Description of the Prior Art Bistable'flueric amplifiers are well known. Most such amplifiers have regions between the control channels and the ,vent channels (known as sidewalls) which are straight. When fluidflows past such sidewalls, aregion-of low pressureis created, which results in a generally convex separation bubble appearing at the sidewall. For example, see U.S.- Pat. No. 3,326,227 for such a bubble.

Such a separation bubble is undesirable for a numberof reasons. It causes a hysterisis effectwith change of input-jet velocity. It also causes variation in the amount of control flow needed to achieve a given switching effect. It causes the amplifier to become load sensitive and to tend to oscillate.

it has been attempted to modify the straight sidewalls into concave walls. For example, see Rechten,'A.'W., Flow Stability in Bistable FluidElements, Proceedings of the Second Cranfield Fluidics Conference, Jan. l967.-I-lowever, it can'be shown experimentally that such concave walls do not improve the stability and pressure recovery of a bistable amplifier.

{SUMMARY OF THE INVENTION The invention is abistable flueric amplifier having convex sidewalls and a concave splitter'plate cusp. The precise optimum values of the various relative dimensions of this amplifi- -.er have been obtained through a long. involved series of experiments.

Use of these optimum values of relative dimensions allows the manufacture and use of a nearly ideal bistable flueric amplifier. Although the prior art contains no known bistable flueric amplifier having convex walls and a concave splitter degree of response.

In a straight-walled amplifier, the vents help to make the amplifier less load-sensitive. In a convex-walled amplifier, these vents have the additional purpose of discharging the low energy boundary layer flow from along thesidewalls and thus to direct the high-energy core flow into the output channel. This boundary layer discharge provides an energy recovery greater than would be calculated by an analysis whichassumed isentropic flow. Thereason for this greater energy recovery is that the pressure recovery in the output channel is thepressure recovery of a flow ata higherkinetic energy than the kinetic energy of thesupply jet.

Had the'relative dimensions presented hereinafter as critical been different from their critical values, the boundary layer development along the sidewalls would have beensignificantly different. This difference would have made it practically impossible toachieve the nearly ideal performance presented herein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view of a convex-walled,.cusped, vented bistable flueric amplifier according to the present invention.

FIG. 2 is an enlarged view of a splitter plate asshown in FIG. I.

'FIG. 3 is an enlarged view of a-convex sidewall as shown in FIG. 1. FIG. 4 is a graph showing pressure recoveryas a function of fluid recovery in the preferred embodiment of the invention.

must be 1. 19 :t 0.03 and the ratio FIG. 5 is a graph showing pressure recovery as a function of the ratio of control flow to jet flow in the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is an overall view of a convex-walled, cusped, vented bistable flueric amplifier according to the present invention.

A fluid power jet is applied to the amplifier through a power channel 1. Control channels 2 and 3 carry control jets which control the direction of the power jet by deflection. The deflected power jet passes between convex sidewalls 4 and 5 to strike a cusp 6 in a splitter plate 7. Vent channels 8 and 9 are provided to each side of the cusp 6.

@The deflected power jet leaves the amplifier via one of the two output channels 10 and 11. Because the amplifier is bistable, substantially all of the output fluid in the deflected power jet leaves the amplifier viaonly one of the output channels, as controlled by the deflection caused initially by a control jet.

This outputfluid does not include the small flow of boundary layer fluid which leaves by the vent channels. When the jet is attached to sidewall 4, there is no flow in. the output channel 1 l, and vice versa.

Cusp 6 has the effect of catching the other (unattached) low energy side of the deflected power jet as it leaves via one output channel and turning the fluid from this edge about to reinforce the deflection.

A number of dimensions of the amplifier are illustrated in FIG. l, as follows:

Figure 2 shows the splitter plate 7 in more detail. In this figure, more dimensions are illustrated as follows:

r=the radius of curvature of the cusp 6 48w=the radius of curvature of a concave section 15 of the splitter plate 6w=half the chord length of concave section 15 5w=the distance from the extended apex 16 of the splitter plate to the center of curvature of cusp 6.

Figure 3 shows the convex sidewall 5 (symmetrical with sidewall 4) in more detail. One additional dimension is given, as follows:

20w=radius of curvature of a sidewall.

Through an involved sequence of experimentation, it has been found that certain of these dimensions have critical values in a limited range for the above-cited nearly ideal performance characteristics. Other dimensions have less critical values-and can assume-a wider range of acceptable values.

Two of the most critical dimensions, expressed in dimensional ratios, are and The ratio w w v I w i-must be 11.03102.

Somewhat less critical is the angle A, which should be 24 1 2". Also less critical is the ratio 5-. which should be 2.5i0.5, and the ratio which should be 1.505: 0.25.

For values differing significantly from these op- :timum values, there is significant deterioration in the opera tion characteristics.

. It can be seen that, given the dimensional ratios set forth, all a of the important dimensions of the amplifier can be specified by specifying the value of w. Amplifiers have been tested for uranging from one-sixteenth to one-half inch. [t is obvious that with a given velocity of fluid flow, it becomes more difiicult to maintain proper operation as w becomes smaller. The velocity is best expressed in terms of Mach numbers and Reynolds numbers.

The amplifier has been successfully tested with Reynolds numbers of 9,750 to 60,000 and Mach numbers of 0.07 to 0.42. Lower numbers, down to Reynolds 4,000, would be usable but not particularly useful for practical purposes. Velocities yielding Reynolds and Mach numbers significantly higher than those given would begin to cause deterioration of the response characteristics. However, as these numbers represent jet velocities much higher than conventionally used, no problem is seen.

As long as the amplifier is scaled with proper geometry and dimensional ratios as given, and with Reynolds and Mach numbers in the given range, the amplifier is insensitive to scalmg.

FIGS. 4 and 5 are graphs representing the response of an amplifier having the disclosed critical dimensions,

where P is the static pressure of the active output channel P, is the supply pressure of the power jet Q is the flow rate in the active output channel Q, is the power jet fiow rate and Q is the fiow rate in the control channel necessary for switching from one bistable state to the other.

In these graphs is termed the pressure recovery I factor. In Figure 4 pressure recovery is shown plotted against fluid recovery for closed control channels and open control channels.

The characteristics shown for closedcontrol channels are substantially constant from fully-blocked to half-blocked operation.

In FIG. 4, it is seen that pressure recovery remains nearly unity for various values of jet velocity for fluid recoveries up to about 50 percent recovery for closed control channels. For open control channels, the pressure recovery is down by about percent over the same range.

This pressure recovery represents a significant improvement (about 40 percent) over the best obtainable recovery from a straight-walled amplifier with closed control channels, which decreases almost linearly from about 70 percent to 40 percent as fluid recovery increases. It is also significantly better than recovery from curved wall amplifiers having dimensional values outside the stated limits.

FIG. 5 is a graph illustrating that the control flow necessary for switching Q, remains a nearly constant percentage of jet flow rate Q,- for all values of pressure recovery in the amplifier having the preferred dimensional ratios.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Iclaim:

1. in a flueric bistable amplifier comprising a power channel for admitting a power jet to said amplifier through a power channel outlet, a pair of control channels for admitting control jets, a pair of vent channels, a pair of outlet channels separated by a splitter plate, and a pair of sidewalls, each sidewall being situated between a respective one of said control channels and a respective one of said vent channels, the improvement comprising:

a. a symmetrical concave arcuate cusp on said splitter plate in the direct path of said power jet when undeflected',

b. a convex arcuate region on each of said sidewalls; I c. said arcuate cusp and arcuate regions being each in the shape of circular arcs; and

d. the width of the narrowest channel between said pair of sidewalls is d, the distance from said power channel outlet to said cusp is s, and the width of said power channel is w, and wherein:

the ratio 5 is between 1.16 and 1.22, and the ratio of is between 10.8 and 11.2.

2. The amplifier according to claim 1 wherein the junction of each of said vent channels with its respectively adjacent output channel has a radius of curvature R and wherein the and 3.0.

3. The amplifier according to claim 1 wherein said cusp has a radius of curvature r and the ratio a; is between 1.25 and 1.75.

4. An amplifier according to claim 1 wherein said splitter plate has an angle A corresponding to the peak-to-peak deflection of the power jet, and wherein the angle A is between 22 and 26.

5. The amplifier as claimed in claim 1 wherein the inside walls of both output channels are concave downstream of the cusp with the radius of curvature of the concave section of the output channel wall being on the order of 48 times the width of the power channel.

6. An amplifier according to claim 1 wherein the junction of each of said vent channels with its respectively adjacent output channel has a radius of curvature R, said cusp has a radius of curvature r, and said splitter plate has an angle of A corresponding to the peak-to-peak deflection of the power jet, and wherein:

ratioof g is between 2.0

a. the ratio is between 2.0 and 3.0;

b. the ratio is between 1.25 and 1.75; and c. the angle A is between 22 and 26.

7. The amplifier according to claim 6 wherein the inside walls of each output channel have concave sections immediately downstream of the cusp with the radius of curvature of the concave sections being on the order of 48 times the width of the power channel. 

